Analytical and preparative centrifuges for use in experimental biology and biochemistry, as well as diagnostic applications, are required to run at high speeds (up to 100,000 revolutions per minute-RPM) in order to accomplish gradient or related separations. The faster the speed, the more refined the separations or the quicker one can complete scientific analysis on the sample as part of an integrated laboratory procedure. High speeds must be attained through the rapid and smooth acceleration, and later deceleration, of the centrifuge rotor, so that biological samples and sample band distributions are not significantly altered and samples are preserved. The speeds attainable by a centrifuge rotor are limited by the stress in the rotor, and maximum amount of kinetic energy that the centrifuge housing and barrier ring may safely contain.
As a rotor is accelerated up to a maximum speed for its rating, defects in the motor, centrifuge rotor, or control system can lead to rotor mishap. Rotor mishap is associated with faulty rotors, motors, or control systems conventionally available for monitoring and controlling the centrifuge rotor speed. In the event that a high speed rotor disconnects from the drive shaft, or otherwise fails to function as designed, such a rotor will be capable of releasing large amounts of kinetic energy. In order to ensure the safety of the user, and the integrity of the centrifuge apparatus, conventionally the steel barrier ring residing within the centrifuge housing surrounds the rotor and motor assembly for the purpose of containment of the rotor in the event of a mishap.
As a preliminary safeguard, various fail safe systems may be installed to cooperate with the centrifuge apparatus to control the speed of the rotor and identify a particular rotor to ascertain whether a given rotor is operating beyond the limitations recommended for its safe use. For example, motor speed may be controlled according to the teachings of U.S. Pat. Nos. 3,436,637, 4,284,931, and 4,286,203 all to Ehret (assigned to the assigneee of this application). Additionally, a method of rotor identification, through the use of optically sensed overspeed discs affixed to each rotor, as taught in U.S. Pat. No. 3,921,047 (assigned to the assignee of this application) allows the centrifuge operating system to detect when a given rotor has reached or exceeded its approved operating rating. Mechanical safeguards, such as a breakaway rotor base, as described in U.S. Pat. No. 4,568,325 to Cheng and Chulay (assigned to the assignee of this application), have been used in an attempt to prevent the release of unexcessive kinetic energy by causing the rotor to safely fail prior to a release of kinetic energy which exceeds the containment limits of the centrifuge housing and barrier ring.
As an alternative, speed control and rotor identification schemes have been developed which uses a magnetic detector to sense a changing magnetic flux generated by a plurality of magnets embedded in the base of each rotor. As the rotor whirls past the magnetic detector, both speed and rotor identification may be ascertained in order to detect rotor operating conditions before abnormal conditions deteriorate into rotor mishap. This detection scheme may use the magnetic signal to detect rotor imbalance and to control rotor speed as a function of the motor timing signals.
Heretofore, no matter how many security and control systems were implemented to assure rotor safety, the ultimate fail safe device has been the conventional steel barrier ring which surrounds the rotor assembly within the centrifuge housing. In the event of rotor mishap, the barrier ring has been designed to contain the forces which arise during rotor mishap, and prevent the rotor from injuring the property or the person of the operator. A heavy barrier lid on the top of the centrifuge cabinet acts as an additional blockage for the containment of any rotor mishap.
Reliance on prior identification, such as rotor I.D. schemes, must not be the only back-up system for speed limiting the rotor, since conventional rotor identification relies on the accuracy of the identification label, which may be improperly installed.